The present invention relates to a method of producing a creasing and/or cutting die, and to a die manufactured by this method.
The invention is particularly concerned with a creasing and/or cutting die which may be slipped over and attached to an outer circumferential surface of a roller of a creasing and cutting machine which produces blanks from cardboard or similar material, which may later be folded along the creases to form a wrapping box or a similar container.
There are already known various dies for accomplishing this task, that is dies which are preferably planar when they are manufactured but which are subsequently bent to conform to the outer circumferential surface of the roller, and then slipped over such surface and attached to such roller so as to share its rotating movement. Generally speaking, such a die includes a relatively thin metal or similar sheet or foil, and is provided on its major surface which will face away from the outer circumferential surface of the roller when the die is mounted thereon, with a plurality of cutting or creasing edges or blades which are adapted to contact an advancing strip of cardboard or similar material and either cut a blank out of the strip, or crease the blank, or both. Either a counter-die is mounted on a counter-roller and cooperates with the die during the cutting and/or creasing operation or the die cooperates directly with the counter-roller. There are also already known various methods for producing such dies and counter-dies.
Before discussing the various methods of producing the dies, and the dies produced by these methods and their advantages and drawbacks, it should be mentioned that the various cutting and/or creasing blades are positioned on their base in accordance with a special system of coordinates, according to markings provided on the base or directly in conformity with the drawing of the blank to be produced during the cutting and creasing operation which is transferred or projected on the major surface of the base. A reducing coefficient must be taken into consideration for the lines which extend in the direction of rotation for the die when mounted on the respective roller to compensate for the deformation of the base and of the blades when bent around the roller.
In one conventional method of producing dies, the die and the counter-die are formed as relatively thin steel plates which are provided with flat webs in a photomechanical etching process. The webs have flat engaging surfaces which, when the dies are mounted on their respective rollers and rotate therewith, contact the exposed major surfaces or the strip material to be severed or creased. These flat surfaces extend parallel to the exposed surfaces of the material in the region of contact therewith, and the associated flat surfaces of the die and counter-die are offset with respect to one another with partial overlapping, so that they exert forces on the material to be cut or creased, which forces result in a squeezing deformation of the material in the vicinity of the respective associated flat surfaces of the webs which, in an extreme situation, results in ripping off of the useless material and production of the useful blank.
However, experience with this kind of dies and counter-dies has shown that they are disadvantageous in various respects. First of all, it will be appreciated that, as a result of the provision of the flat webs having the flat engaging surfaces which are offset with respect to one another on the die and the counter-die, respectively, and particularly as a result of the fact that the flat surfaces are so arranged that they never come into contact with one another, the material cannot be severed along an accurate cutting line as would be the case if the material were cut with a different cutting tool which would be provided with a sharp cutting edge cooperating with a hard counter-surface. Rather, the material is only squeezed between the flat surfaces of the die and the counter-die which results in many materials in uneven peripheral edges of the so-produced blank. Furthermore, the production of such dies and counter-dies requires the availability of a special equipment capable of producing such dies and counter-dies in a very precise manner and with only minute tolerance deviations from the desired shape of the webs and the flat surfaces thereof, such a special equipment not always being available to the user of the cutting and creasing machine. This, of course, is very disadvantageous since, whenever a new production line is to be initiated, the new die and counter-die must be ordered from a supplier, which results in unnecessary delays. Such problems are also encountered when worn-out dies and counter-dies are to be replaced. Also, the photomechanical process of producing such dies is relatively expensive, which contributes to a relatively high cost of the dies and the counter-dies. Another drawback of such a method of producing dies resides in the fact that the webs with their flat surfaces are integral with the die substrata so that, when only some of the webs are worn out or damaged, it is impossible, or possible only with an excessive effort and a high cost, to replace the worn-out or damaged webs with new ones. Thus, in many instances, it is less expensive to replace the entire die or counter-die, rather than to attempt to repair the same which, of course, reduces the useful life of the die.
There are also already known different creasing and/or cutting dies in which the die again includes a relatively thin metal sheet, and wherein pins are connected to such a sheet, for instance, by spot welding. Cutting and creasing blades, which are curved to conform to the shape of the metal sheet when connected to the respective roller, are then connected to and/or clamped by the pins and thus attached to the metal sheet. Such dies are not only known from the packaging industry, but find their most advantageous use particularly in the machines for punching and cutting metal, particularly steel, strips.
In such dies, where the cutting or creasing blades are clamped by the pins and where the dies rotate together with the respective rollers, other disadvantages are present. So, for example, since the pins have to be connected to the metal sheet, for instance, by spot welding, the dimensions thereof cannot be miniaturized below a certain level, particularly since the pins must be sufficiently rigid and be securely connected both to the metal sheet and the cutting or creasing blade mounted thereon. This, in turn, results in the need to make the cutting or creasing blades relatively high in order to extend to a sufficient extent radially outwardly beyond the pins. However, because of the relatively large dimensions of the blades, and particularly because of the relatively large height thereof, the blades are often prefabricated so as to have a curved configuration in their longitudinal direction before they are mounted on the metal sheet. This is necessary because of the fact that the relatively large dimensions of the blades result in their high resistance to bending, so that it is all but impossible to mount the blades on the sheet as long as it is still planar, and then bend the sheet with the blades mounted thereon. Thus, the usual method of assembling such a die is to mount the metal sheet with the pins thereon on the respective roller, and only then to connect the respective blades to the proper pins. Since the assembling of the die is accomplished directly on the roller, it requires that the creasing and cutting machine be put out of operation for an extended period of time which, of course, is very disadvantageous.
However, the production of the spatially curved blades is a difficult and time-consuming task. This is caused by the fact that the blades are relatively high, so that they not only have a high resistance to bending, but also there exists the danger that undesirable deformations of the blades, particularly out of their general planes, will occur during the bending operation; thus, the blades will more often than not extend only approximately radially outwardly of the die and thus of the roller, which adversely affects the accurate operation of the creasing or cutting machine. As a result of this inaccuracy, the roller with the die thereon may not be dynamically balanced, and the products obtained during the cutting or creasing operation may be of less than desired configurations and appearances.
On the other hand, it is possible in this arrangement to simply replace blades which are worn-out or damaged beyond repair, even though only while the machine is in standstill. When some of the blades are only partially worn out or damaged, it is desirable to lift the metal sheet in the region of such wearing-out or damage in order to be able to continue the operation of the machine with the same die so long as it is still usable. This is usually done by putting inserts between the roller and the metal sheet in such a region. However, in this particular arrangement, such extension of the useful life of the partially damaged or worn out die is all but impossible because of the high resistance of the blades to bending. Thus, the utilization of this arrangement is very limited. Other disadvantages of this arrangement are that, when the pins are to be distributed on the metal sheet and welded thereto in an automatic welding machine using a control program for controlling the operation of the automatic welding machine, the program as well as the welding machine must be very precise which increases the expenditure in connection with the production of such a die, and that it is impossible to visually supervise the exact position of the blades during the assembling operation and afterwards. The advantage of this die, which cooperates with a counter-roller so that the material to be cut and/or creased passes between the die and the counter-roller, is that the severing lines of the blank are rather accurate and the appearance of the blank better than when the previously discussed dies are used.
Other dies may also be used, the blades of which basically resemble those used in reciprocating presses for cutting blanks out of steel or other metallic strips. Such blades are in this case embedded in or otherwise connected to initially curved shells made of wood, metal or a synthetic plastic material, which shells are then assembled on and connected to the respective roller so as to share the rotation thereof. In such an arrangement, the blades operate similarly as discussed in connection with the previous prior art, that is they cooperate either with a counter-roller or with a flat surface, the material to be severed or creased passing between the shells and the counter-roller or the flat surface.
Similar problems as those discussed in connection with the previously mentioned arrangement are also encountered in the die according to this embodiment where the blades are accommodated in and connected to the curved shells of metal, wood or synthetic plastic material. Even in this arrangement, the assembling of the dies must be performed in two phases, the first phase involving the connection of the base plate -- that is of the shells -- to the roller, and the other phase involving pressing the blades into the base plate. This base plate is usually formed with prefabricated grooves into which the blades are pressed, and the accuracy of the positions of the blades will to a large extent depend on the accuracy with which the receiving grooves have been prefabricated in the base plate. However, very often it is impossible to prefabricate exact grooves in the curved base plate, so that it cannot be assured that the actual positions of the blades will conform to the desired positions thereof. Furthermore, since the engagement of the blades with the grooves is not secure enough, it is necessary to provide additional attachment elements extending, for instance, through perforations in the sides of the blades, which then secure the blades to the base plate and prevent their displacement out of the respective grooves. As discussed above in connection with the previous arrangement, the adjustment of the positions of the worn-out or damaged blades is also very difficult if not impossible.
There are also already known different dies for use in creasing and cutting machines of the type employing rotating rollers between which the material, such as cardboard, passes to be treated, which dies utilize blades which are generally triangular in cross-section and which are connected to the metal sheet or other base by brazing, soldering, glueing or attaching by screws or similar connectors. The roller which is equipped with such a die can cooperate with a counter-roller in a conventional manner. The material to be treated enters the gap between the die and the counter-roller and thus is pressed against the counter-roller and severed, embossed, creased or the like by the exposed working edges of the triangular blades. In the event that the blades which may be of various shapes are directly connected to a base by spot-welding, brazing or soldering, the heat transmitted to the base during such operations results in deformation of the base owing to the non-uniform thermal treatment of the base and thus the generation of local stresses. During the operation of the machine, relatively high forces alternatingly act on the blades, which may result in the destruction of the connection between the blades and the base, particularly when such a connection is obtained by spot welding. In order to obtain rotational symmetry of the die and particularly of the cutting edges of the blades, it is necessary to adjust the positions of the blades with respect to the base or to perform other finishing operations. However, since the base itself has been deformed during the soldering, brazing or spot-welding operation, the time and labor expenditure for such a finishing operation is excessive. A particular disadvantage of the dies which are manufactured according to this method is that the damaged or worn-out blades can be replaced only with difficulty and at high cost.
In the event that the creasing or cutting blades are connected to the base by glueing, the main disadvantage of this method of producing the die is that the glued connection has relatively low resistance to the forces which act on the blades during the operation of the machine, so that the glued connection will disintegrate within a relatively short period of time. More particularly, the layer of the glue, adhesive, or other bonding agent dissociates itself either from the base or the blade and peels off. This, of course, reduces the useful life of the die.
A further modification of the just-described die which suffers of the same drawbacks as discussed above is that the base is a transparent foil. Blades, which are substantially triangular in cross-section, are bonded to the foil. It is possible to attach the foil to the roller first, and in this case the blades are curved so as to substantially correspond to the outer curvature of the foil mounted on the roller, and then positioned thereon and bonded thereto. Alternatively, the blades may be straight and be bonded to the foil in its planar state, and then the foil may be bent together with the blades bonded thereto so as to conform to the circumferential surface of the roller and be attached thereto. The operation of this die is the same as previously discussed, and the danger of disintegration or peeling-off of the bonded connection is still present.
Finally, there is also already known a method of producing the die in which the creasing or cutting blades, each of which is formed with an angularly bent foot, are directly connected to a metal sheet jacket which is subsequently driven into rotation during the cutting or creasing operation. In this method, the blades must be positioned on the jacket in accordance with a marking on the jacket or in accordance with a drawing, which is very time-consuming and, moreover, which is very inaccurate so that the blades are connected to the jacket in positions which to a greater or lesser degree deviate from the desired positions. This, in turn, means that the shapes of the thus-produced blanks will deviate from the desired shapes, which is particularly disadvantageous if the blanks are to be used for producing boxes or packages in an automatic packaging machine.
It may be seen from the above discussion of the prior art dies and methods of producing dies that no method of producing dies is known at present which renders possible the formation of the die in a plane, that is in its developed form, and its subsequent bending around the roller and attachment of the same thereto, which die would also achieve satisfactory results in terms of the preciseness of the severing and/or folding lines on the blanks.